A vascular aneurysm is a result of lesion or injury in the arterial wall, which forms a localized or diffuse dilatation or bulge on the arterial wall and mainly shows as an expansile and pulsatile tumor. Aneurysms may occur in any blood vessel and include abdominal aortic aneurysm, cerebral aneurysm, peripheral aneurysm, visceral aneurysm, etc. The wall of an aneurysm is thin and fragile, making it prone to rupturing.
Besides conventional conservative or surgical treatments, the interventional treatment is currently an important therapy for aneurysm. In the interventional treatment, it is a widely-used approach to place embolic materials such as detachable balloons, coils, etc. into the body of an aneurysm by using a catheter so that the speed of blood flow in the body of the aneurysm may be significantly reduced or even stopped. By this means, a thrombus may be gradually formed to embolize the body of the aneurysm in order to prevent the aneurysm from rupturing.
However, at least the following defects exist when the interventional embolization treatment mentioned above is adopted for large (maximum diameter of more than 10 mm) or huge (maximum diameter of more than 25 mm) aneurysms. First, it is required to use embolic materials such as coils to densely fill the aneurysm. However, large or huge aneurysms are often wide-necked aneurysms. In such cases, coils as the embolus are very easy to project out into the parent artery carrying the aneurysms, which may cause stenosis or even occlusion to the parent artery. Taking the cerebral aneurysm as an example, this may lead to serious consequences such as cerebral ischemia or even cerebral infarction. Second, the mass effect is common to large or huge aneurysms. The aneurysms may become larger, thereby compressing surrounding viscera and tissues and affecting their physiological functions. Although filling an aneurysm with coils may embolize the aneurysm, it cannot eliminate the mass effect caused by the aneurysm or may even worsen the mass effect.
One type of flow diversion device that is based on a densely-netted vascular stent (only simply called “stent”) came out in recent years. This type of flow diversion device may effectively overcome the above-described defects of coil embolization in treating large or huge aneurysms. After implanted to the parent artery, the flow diversion device may interrupt blood flow from the parent artery to the aneurysm by the fine mesh of the stent and cause blood in the aneurysm to clot so as to form a thrombus, thereby occluding completely the aneurysm. In addition, the flow diversion device may be provided for vascular endothelial cells to climb thereon. After the flow diversion device is covered by vascular endothelial cells, a permanent biological sealing may be formed on the neck of the aneurysm, which may help the parent artery to recover and become a normal vessel.
However, there are still defects in the stent-based flow diversion device as described above. Taking the Pipeline™ embolization device of Medtronic PLC as an example, the stent is configured as being rotatable around the core component of the flow diversion device. Accordingly, torsional stress may be generated between the stent and the core component (e.g. the core wire) while the stent is pushed to the lesion through circuitous and curved vessels. As a consequence, when the compressed stent arrives at the lesion, it may not be able to deploy automatically due to the effect of the torsional stress. Since the torsional stress may be unpredictable, failure in deploying the stent might still exist even if the deploying is manually done by twisting the core wire.
In addition, sharpness of a radiographic image may be limited for vessels of small diameters, which in turn may influence precision in the position where a stent is placed. In the case of the Pipeline embolization device, it would be very difficult to pull the deployed stent back to the catheter and re-adjust the placement position when the deployed stent is found at an unsatisfactory position.
After problems like a failure in deploying the stent or an unsatisfactory placement position of the stent occur, it may need to take the entire Pipeline embolization device out, which may not only cause the expensive device out of use but also cause injury to the patient due to the larger diameter of a deployed stent.